The above image was shown on all Sony Pictures computers(Business2Community)

Sony Pictures Entertainment employees worldwide have been ordered to disconnect their computers and not access email, after the studio was struck by a malicious hacker attack which infiltrated the company's network and threatened to publish "secrets".

The hack was first noticed on 24 November when an image showing a skeleton and the message "Hacked by #GOP" was shown on every computer in Sony Pictures' New York office; it is claimed the image then spread to every Sony Pictures office across the US, according to a Reddit user speaking to Business2Community.

The message adds: "We've already warned you, and this is just a beginning. We continue till our request be met. We've obtained all your internal data including your secrets and top secrets. Determine what will you do till November the 24th, 11.00pm (GMT)."

Guardians of Peace, the group believed to be behind the attack, has leaked a large ZIP file containing "two massive lists," according to Geek.com, detailing what data has been stolen. It is claimed this includes Excel documents and ZIP files containing passwords from Sony Pictures' finance department.

Stolen documents include 'Insurance for security breaches'

A poster on Reddit who claims to have downloaded the files say they are two "huge" lists of document names. "The first one is 600MB the second one 388MB...I guess is the list of files they hacked from Sony. There is a lot of interesting things in the list from movies...mostly docs and Excels."

A Sony source told Deadline: "We are down, completely paralyzed," while a Sony Pictures spokesperson told several publications: "We are investigating an IT matter."

As the company asks all employees to switch off their computers and disconnect mobile devices from office Wi-Fi, a second Deadline source said the situation may take anywhere between one day and three weeks to resolve.

The hack soon spread, as images branded with "Hacked By #GOP" appeared on the Twitter accounts of Sony Pictures films, including Stomp The Yard, Starship Troopers, and Soul Surfer."

Bloomberg, citing an anonymous source, claims the hack may be a blackmail attempt and linked to a group called Guardians of Peace, but no further details were given about why the hack has taken place and what the hackers are trying to achieve.